Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.87   7.626%   $253.8574   $253.86   $253.85   $253.90  
  Purchase #2 $219.55   13.255%   $248.6514   $248.65   $248.65   $248.70  
  Purchase #3 $162.87   10.106%   $179.3296   $179.33   $179.35   $179.30  
  Purchase #4 $93.89   4.493%   $98.1085   $98.11   $98.10   $98.10  
  Purchase #5 $161.65   12.608%   $182.0308   $182.03   $182.05   $182.00  
  Purchase #6 $92.43   3.599%   $95.7566   $95.76   $95.75   $95.80  
  Purchase #7 $9.96   11.563%   $11.1117   $11.11   $11.10   $11.10  
  7 purchase totals = $976.22       $1,068.8460   $1,068.85   $1,068.85   $1,068.90